On 7/23/20 9:25 AM, Sean Christopherson wrote: > How would people feel about taking the above two patches (02 and 03 in the > series) through the KVM tree to enable KVM virtualization of CET before the > kernel itself gains CET support? I.e. add the MSR and feature bits, along > with the XSAVES context switching. The feature definitons could use "" to > suppress displaying them in /proc/cpuinfo to avoid falsely advertising CET > to userspace. > > AIUI, there are ABI issues that need to be sorted out, and that is likely > going to drag on for some time. > > Is this a "hell no" sort of idea, or something that would be feasible if we > can show that there are no negative impacts to the kernel? Negative impacts like bloating every task->fpu with XSAVE state that will never get used? ;) I thought KVM had its own vcpu->arch.guest_fpu buffers which mirrored the size and format of task->fpu. Can we have KVM support today without task->fpu support? I see some XSS munging in the KVM code so I think this might be *possible*, but I don't see all of the plumbing that would make it actually work.
